How Sleep Resets the Brain

So just what is the brain doing during sleep? We know sleep is necessary to cognition, glucose control, weight, memory, even life asleep. But what’s really going on in there?

The layers of information that control and constantly renew the human body are strikingly complex. One of the most useful theories to explicate how was developed by Giulio Tononi and Carla Cirelli, two brilliant people who decamped from Turin to work at the University of Wisconsin-Madison since 2003. Their synaptic homeostasis hypothesis argues that learning – necessary for life – is difficult and biologically expensive. That during our waking hours the synaptic connections between brain cells, powered by long term potentiation, get tighter, stronger and bigger. So big, that they need pruning and resetting if they are continue to work.

And that is partly the work of sleep. Big fat nerve cell connections are remade, broken and reformed, pruned and reorganized. The fat synapses of day become the thin synapses of dawn.

Accomplished through the medium of sleep.

There’s been lots of studies looking at this hypothesis in animals. Tononi and Cirelli have worked for many years from the molecular to the full mammalian model, including innovative EEGs that promise to pick up far more than the standard formats of today. But the work has mostly been done in animals. What about people?

Sleepless in Freiburg

A group headed by Christoph Nissen at the University of Freiburg (Germany) decided to try. You can’t do to people what you do to rats and mice. More indirect, creative scientific solutions are called for.

So the researchers took a group of young people and gave them transcranial magnetic stimulation (TCMS or TMS,) a remarkably useful and increasingly specific technique, to stimulate parts of their brain. Then they kept them up all night. Other electrical stimulation techniques were used to test memory.

Surprisingly, following sleep deprivation, TCMS more readily provoked specific muscles to contract than when people had a full night’s sleep. Their brains remained “highly stimulated,” making it easier for muscles to jump.

It’s not just muscles that change. People are far more prone to shakier, impulsive decisions when sleep deprived. Since much of the population is regularly sleep deprived, that’s a big problem.

The other part of the experiment, checking stimuli that normally lead to memory formation, showed the expected deleterious effects of sleep loss. So what does this understanding of brain resetting during sleep mean to the rest of us?

Secrets of Sleep Deprivation

Sleep deprivation is not necessarily bad. For many years, researchers have known that sleep deprivation makes depressed people less depressed.

The effects are often remarkable. In one night of sleep deprivation, patients may look better as a group than after months of antidepressants or Cognitive-Behavioral Therapy.

That’s what has Nissen excited. If you can so quickly reset the brain with sleep loss, can’t there be a way to do it without keeping people up all night?

From a therapeutic standpoint, there better be a way. Sleep deprivation can rival the now heralded ketamine for making highly depressed people less depressed. But there’s a critical obstacle. Let depressed people sleep just a few minutes, and the whole anti-depressant improvement washes out. Very rapidly patients lose all their gains. And they will have to sleep sometime. So new approaches are needed.

The Next Moves

It has been a long slog to teach researchers that the body is a continually renewing information system, or system of systems. That health is the result of the body remaking itself quickly and elegantly, rather than of “breaking down,” is still difficult for researchers to accept. Clinicians, transfixed by homeostasis and medical care that is overwhelmingly attached to numbers defining homeostatic states, have a particularly hard time seeing the body as constantly, ceaselessly remade. The binary dichotomy of health and disease, normal and abnormal, is much easier for clinicians to accept. A blood pressure of 131/81 is hypertension. A blood pressure of 130/80 is normal. That blood pressure normally shifts 15% over the 24 hour day is a concept too difficult for many to assimilate.

The public has an even harder time.

But things are changing. Tononi’s vision of sleep makes our present “understanding” of the five stages of sleep look and feel absolutely primitive. Different parts of the brain are performing different functions every second, making the whole show new all the time.

And that’s true during wake as well as sleep. It turns out illness is a failure to regenerate, rather than a result of degeneration. Sleep resets the brain, and every other organ, so that some very specific regenerative functions can take hold. That information is the real substrate of genes and biology. Species and their organisms only survive by constantly learning, updating, and renewing themselves to contend with a constantly updated, renewed, and changed environment.